1. Field of the Invention
This invention relates to a sleeve for an optical fiber connector and a fabricating method therefor, for detachably connecting optical fibers mutually while holding them in a state in which ferrules coaxially formed at ends of the optical fibers are matched on a same axial line.
2. Background of the Invention
Optical fibers are used as optical wave guides for optical transmission of information by the medium of light.
The optical fiber, for example, an optical fiber 1 having a single core as shown in FIG. 3 is composed of a fiber core wire 4 comprising a core 2 and a cladding 3 differing in its refractive index from the core and made of high purity quartz glass or the like, and an outer covering 5 for coating said fiber core wire 4 being made of nylon, ultraviolet setting resin or the like.
The optical fiber 1 is manufactured in various lengths, and for constructing an optical fiber cable route, a plurality of optical fibers are semipermanently connected by fusion or adhesion to obtain an optical fiber cable length having a specified distance. However, when connecting the optical fiber 1 to an optical apparatus or when connecting the optical fibers 1 together at the time of construction, maintenance, experiment or other uses in an optical communication system, an easily detachable optical fiber connector is used.
Such an optical fiber connector is designed to connect the optical fibers 1 mutually by inserting plug ferrules 6 formed at the ends of respective optical fibers 1 into both ends of a sleeve 7 as shown in FIG. 4. The structure of the sleeve 7 is further described below.
The plug ferrule 6 is formed by laminating wear resistant materials such as synthetic resin, ceramics and metal properly to the end of the optical fiber 1, the plug ferrule 6 being coaxial with the fiber core 4 of the optical fiber 1. The sleeve 7 is a tubular member having an approximately C-shaped cross-section and having a slit 8 formed on the outer surface thereof running the entire length of the sleeve 7 in the axial direction thereof. The inside diameter of the sleeve 7 is slightly smaller than the outside diameter of the plug ferrule 6.
For mutual connection of optical fibers, it is enough to insert the plug ferrules 6, 6 formed at respect ends of the optical fibers 1, 1 into the sleeve 7 until they collide with each other. As a consequence, the sleeve 7 is slightly widened by the insertion of the plug ferrules 6, 6, therein and grips the outer surfaces of the plug ferrules 6, 6 by its own elastic restoring ability. At this time, the sleeve 7 and the plug ferrules 6, 6 are positioned coaxially, and therefore the fiber core 4, 4 of the optical fibers meet end to end, and are connected without any axial deviation, bending or folding.
To disconnect the optical fibers 1, 1, the plug ferrules 6, 6 are simply pulled out of the sleeve 7.
According to conventional practices, the sleeve 7 is manufactured in steps, as shown in FIGS. 6 (a) to (d). For example from one end of a phosphor bronze bar 9 measuring 3 mm in outside diameter and 1 m in length, a hole 10 measuring 2.5 mm in diameter having an effective depth of 10 mm or more coaxially along the axial direction is opened by cutting with a drill. This bar 9 is cut off, and a tubular member 11, 3 mm in outside diameter, 2.5 m in inside diameter, and 10 mm in length is fabricated, and a 0.5 mm wide slit 8 is formed along the entire length thereof in the axial direction along one side face of the tubular member 11.
However, the sleeve for an optical fiber connector manufactured according to the above method involved the following problems.
First, when repeated detachment and attachment of the plug ferrules 6, 6 inside the sleeve 7 is performed, material fatigue occurs as a result of repeated elastic deformation of the sleeve 7, and residual deformation in the diameter occurs, thereby permanently expanding the sleeve, and the gripping force on the plug ferrule 6 is consequently lowered. When the lowering of gripping force was measured by an experiment for checking the changes in the pulling load required when withdrawing the plug ferrule 6 from the sleeve 7 using a sleeve 7 made of phosphor bronze, after 100 repetitions of detaching and attaching the plug ferrule, the pulling load was lowered 60 to 70% from its initial value.
Such deformation of the sleeve 7 and consequent lowering of its gripping force may cause, when the optical fibers 1, 1 are connected, axial deviation as shown in FIG. 7, or increase of optical loss due to folding or bending as shown in FIG. 8, or the plug ferrule 6 may completely drop out of the sleeve 7.
Furthermore, such deformation may result in inspection or measurement errors during the inspection or measurement of equipment, when a particularly high frequency of detaching and attaching of the optical fibers is required. It has been desired to solve the problem of deformation of the connecting sleeve.
Accordingly, one attempt to solve the aforementioned problems could involve fabricating the sleeve 7 with a large gripping force in anticipation of the lowering of its gripping force over time. But in such a case, an enormous force is needed to initially detach and attach the plug ferrules 6, 6 and may also lead to accidental breakage of the optical fiber 1.
Furthermore, since the sleeve 7 is fabricated, as mentioned above, by repeatedly drilling, cutting and slotting the long bar 9, the manufacturing cost becomes extremely high.